1. Field of Invention
This invention relates generally to a power unit and more particularly to a novel power unit for medical and like stools and chairs, which can be selectively extended and retracted by the operator and comprises a ram, a cylinder into which the ram telescopically reciprocates, a tank encircling or adjacent the cylinder and the ram thereby providing a reservoir of oil pressurized by air for telescopically changing the effective length of the unit, a plastic control valve, a plastic bearing and hydraulic seels to prevent leakage of oil.
2. Prior Art
Power units used as stools and chairs and accommodating extension and retraction of a ram telescopically within a cylinder have heretofore required expensive high tolerance metal parts throughout including a complex metal control valve together with extensive actuator structure and a bulky cone-shaped reservoir-forming tank concentrically disposed at the top of the ram in which the control valve is inaccessibly disposed and operably below the pressurized oil level in the reservoir. Because of flaws in tubular material used to manufacture such power units, among other reasons, oil leakage frequently occurs creating serious operational and cleanliness problems.
In view of the foregoing, power units of the type in question are in need of improvement to provide better reliability, lower costs, better valve access for repair, simpler actuation, easier connectability to a stool seat, less bulk and weight and improved configuration, and elimination of hydraulic leakage.